Partial molar properties of homologous dicarboxylic acids in aqueous acetone solutions at different temperatures

Transcription

1 Indian Journal of Chemistry Vol. 35A, March 1996, pp Partial molar properties of homologous dicarboxylic acids in aqueous acetone solutions at different temperatures UN Dash & B K Mohantv Department of Chemistry, Utkal University, Bhubaneswar Received 30 January 1995; revised 12 May 1995; rerevised 2 August 1995; accepted 10 October 1995 The partial molar volumes of oxalic, malonic, succinic, glutaric and adipic acids have been determined in water and water + 5, + 10, + 20, + 30 and + 40 wt % acetone mixtures from density measurements in varying. ranges of concentrations at four different temperatures ranging from K. The density data have been analysed by means of Masson equation. The data have been used to obtain partial molar volumes, coefficients of thermal expansion and partial molar expansibilities of the acids in these solvents. The results reveal the nature of solute-solvent interactions in these solvents. In an earlier work", we had reported the effect of increase in chain length upon the change in apparent and partial molar volume and expansibility of the sodium and potassium salts of fatty (homologous monocarboxylic) acids in formamide. While the influence of CH 2 groups on volume changes has been studied in detail in water", less considerations have been given to such an effect in mixed solvents. This led us to carry out studies on homologous dicarboxylic acids in mixed aqueous medium. In this work, we report data for five homologous dicarboxylic acids [viz., (CHz )x( COOHjz, where x = 0, 1, 2, 3, or 4] in water and water + 5, + 10, + 20, + 30, and + 40 wt % acetone ranging from K. The results have been discussed in terms of solute-solvent interactions. Materials and Methods Oxalic (BDH, AnalaR), malonic (E. Merck, GR), succinic (BDH, AnalaR), glutaric (Fluka AG) and adipic (SRL, Pure) acids were kept in a vacuum desiccator over anhydrous calcium chloride until required. Acetone (BDH, AnalaR) was further purified by the literature method. Conductivity water (sp. condo S em -1) was used for preparing water + acetone mixtures. The acetone content in the mixed solvents was accurate to within ± 0.01 %. The solutions of the acids in water and water + acetone mixtures were prepared by weight. The densities were determined pycnometrically (uncertainty ± 1 x 10-4 & ml : 1). The density measurements were made in a water bath whose temperature was controlled to ± 0.05 K. Experiments were repeated at least 5 times for each solution, and the average was taken as the final density value. Results and Discussion The densities d of acid solutions in water and various water + acetone mixtures at different temperatures were used to convert molalities m to molarities e by the relation.' (1), e= md( mm2tl... (1) where M2 is the molecular weight of the acid. The densities of the ternary solutions can be represented as a function of e by empirical Eq. (2), d = do + A e + Be (2) where A = (M 2 - do (N), B= Svdo, and d.{) is the density of the corresponding pure solvent. The values of do, the density of the solvent mixtures, are recorded in Table 1. The apparent molar volume tpvof the acids was calculated by the relation" (3) tpv= 1000 (edo)-i (-do- d)+ Mzd o -I... (3) It was found that tpvvaried linearly with e 112. The tp" data were fitted by a method of least squares to Masson equation" (4 ) tpv= tpv o + S; e 112. (4) to obtain tpv o and Sv. The values of tpv o and S; are given in Table 1 for the studied acids in different solvents at four temperatures.

2 DASH et al.: PARTIAL MOLAR PROPERTIES OF DICARBOXYLIC ACIDS IN AQ. ACETONE 189 Table 1- Values of ;vo (ml mor ') and S; (ml 312 mol- 312) for homologous oxalic acids in water and water + acetone (5, 10,20,30 and 40 wt %) mixtures at different temperatures ;vo s, ;~ s, ;~ s, (0%,0.9991) (5%,0.9865) (10%,0.9742) K 36.2(9) 16.0(5) 32.1 (9) 16.8(7) 30.3 (9) 17.5 (9) 47.1 (9) 16.1 (6) 42.7(9) 16.7(7) 40.6(9) 17.1 (8) 57.9(9) 16.2 (7) 54.6 (9) 16.7(8) 52.7 (9) 17.1 (8) 69.3(9) 15.9 (7) 64.8(9) 16.3 (8) 63.0(9) 16.8 (9) 80.1 (8) 15.4 (7) 74.5 (8) 16.1 (7) 72.0 (9) 16.1 (9) (20%,0.9506) (30%,0.9281) (40%,0.9066) 26.3 (10) 18.9(8) 23.0(11) 19.9(9) 18.0(11) 21.5 (9) 36.7 (to) 18.6(9) 32.4 (10) 19.8(8) 27.4(11) 21.3 (9) 47.0(10) 18.3 (8) 43.9(10) 19.6 (8) 38.0 (11) 21.0 (9) 57.3(9) 18.0 (7) 54.1 (to) 19.0(9) 48.6 (11) 20.5 ( (9) 17.6 (7) 63.9 (to) 18.7 (8) 59.1.(11 ) 19.9 (8) K (0%,0.9970) (5%,0.9838) (10%, ) 37.4 (9) 16.7(6) 33.2 (9) 17.2 (7) 31.4 (to) 17.7 (8) 48.3(9).1fi.4(6) 43.8 (10) 17.2(6) 41.7 (10) 18.0(7) 59.1 (9) 16.7(7) 55.8 (9) 16.9(7) 53.8 (9) 17.2 (7) 70.9(9) 16.0(6) 66.0(9) 16.8(7) 64.2(9) 16.5 (7) 81.5 (9) 15.8(6) 75.8 (9) 16.0(7) 73.3 (9) 16.4 (7) (20%,0.9459) (30%,0.9224) (40%,0.8999) 27.4(10) 19.0(8) 23.8 (11) 20.0(8) 18.7(11) 21.1 (9) 37.6 (10) 18.8 (8) 34.2 (10) 19.3(8) 28.1 (11) 21.1 (9) 48.0(10) 18.3 (8) 44.8 (10) 19.6(8) 38.8 (11) 20.6(9) 58.3 (10) 18.0(8) 55.1 (10) 19.2(8) 49.5(11) 20.1 (8) 68.8(9) 17.8(7) 64.9(10) 19.1 (8) 59.4(10) 19.7(9) K (0%,0.9940) (5%,0.9799) (10%,0.9662) 38.7(9) 16.6(6) 34.3(9) 17.3(7) 32.4 (to) 17.7(8) 49.6(9) 16.1 (7) 44.9(9) 17.0(7) 42.7(9) 17.6(8) 60.4(9) 16.4 (7) 57.0(9) 16.7(7) 54.9(9) 17.3(8) 71.9 (9) 16.3(7) 67.2(9) 16.6(7) 65.4 (9) 17.0(7) 82.8(8) 16.0(7) 77.1 (9) 16.5(8) 74.5 (9) 16.7(7) (20%,0.9398) (30%,0.9150) (40%,0.8914) 28.2 (10) 18.9(8) 24.5 (11) 19.9(8) 19.3 (11) 21.2 (9) 38.S (10) 18.6(8) 35.1 (11) 19.7(8) 28.8 (11) 20.9(9) 49.0(10) 18.2 (8) 45.7 (10) 19.4 (9) 39.7(11) 20.1 (8) 59.3 (to) 18.0(8) 56.0 (11) 19.5 (8) 50.4 (11) 20.1 (8) 69.9(9) 17.6 (8) 69.9(10) 17.9(8) 60.4 (11) 19.7(9) (Contd)

3 190 INDIAN J CHEM, SEe. A, MARCH 1996 Table I- Values of." (ml mol-') and S, (m(1/2 mol- 3/2) for homologous oxalic acids in water and water + acetone (5, 10,20,30 and 40 wt %) mixtures at different temperature" - Contd.,o s, ~) S, ~ S, K (0%,0.9905) (5%,0.9755) (10%,0.9610) 39.9(9) 16.8 (7) 35.4(9) 17,5 (8) 33.4 (10) 18.0(8) 50.1 (9) 16.7 (7) 46.0(9) 17.3 (8) 43.8 (10) 17.8 (8) 61.7 (9) 16.4 (8) 58.1 (9) 17.0(8) 56.0(9) 17.3(8) 73.2 (9) 16.3 (8) 68.4 (9) 16.6 (8) 66.5 (9) 17.2 (8) 84.1 (9) 15.9 (8) 78.4 (9) 16.4 (8) 75.7 (9) 16.9 (8) (20%,0.9332) (30%,0.9069) (40%, ) 29.1 (11) 20.1 (8) 25.3(11) 20.3 (9) 19.9(12) 21.7 (9) 39.4(10) 18.9 (9) 35.9 (11) 20.1 (9) 29.6 (12) 21.3 (9) 49.9 (10) 18.6 (9) 46.5(11) 20.0(9) 40.5 (11) 21.0 (9) 60.3 (10) 18.1 (9) 56.9 (10) 19.3 (9) 51.3(11) 20.9(9) 71.0(10) 18.1 (9) 66.9(10) 18.6(9) 61.2(11) 20.2(9) 'Values here are temperature, wt % acetone and d'' in g rnl " I. The figures in parentheses in.o and S. are the standard deviations in the order of 10 - I. Table 2-Values of ~(ml mol-i) and SE (ml 312 mol- 312 ) for homologous oxalic acids in water and water + acetone (5, 10, 20, 30 and 40 wt %) mixture at different temperature' (0%,2.856) (5%,3.697) (10%,4.527) #. x SE X 10 2 #. X 102 -SE X 10 2 #. X SE X ~ K 10.1 (15) 2.8(14) 12.9(5) 1.2 (12) 19.8(4) 0.8(4) 10.2 (15) 2.9(14) 13.4 (15) 2.8 (24) 20.3 (13) 2.6 (12) 10.3(15) 2.8 (14) 13.7 (14) 2.7(23) 20.6 (11) 2.0 (12) 10.4 (15) 2.8 (14) 14.0(15) 2.8(23) 21.1 (13) 2.5 (12) 10.6(15) 2.8 (14) 14.3 (15) 2.9 (24) 21.4 (12) 2.6 (12) (20%,6.091 ) (30%,7.596) (40%,8.990) 20.3 (2) 0.7 (7) 20.9(1) 0.2 (1) 21.4 (5) 1.1 (7) 21.2 (13) 2.4 (7) 21.8(14) 2.8 (10) 22.4 (10) 1.9(10) 21.5 (12) 2.3 (10) 22.5 (11) 2.2(11) 22.9(10) 2.0(10) 22.3 (12) 2.3 (1) 23.2 (11) 2.6 (11) 23.5 (9) 1.9 (10) 22.8(12) 2.3(12) 23.8 (11) 2.1 (ll) 24.4 (9) 1.3 (10) K (0%,2.861). (5%,3;707) (10%,4.543) 10.2(14) 3.0 (8) 13.1 (5) 1.2 (8) 20.2(4) 1.0 (6) 10.3 (15) 2.9(8) 13.6 (15) 2.8 (11) 20.7 (14) 2.6 (10) 10.4 (15) 2.9 (9) 13.8 (12) 2.4(12) 21.0(6) 1.0 (13) 10.5 (15) 2.8 (10) 14.1 (13) 2.6(19) 21.5 (14) 2.6 (12) 10.6(15) 2.8 (10) 14.5(14) 2.8 (19) 21.8 (13) 2.4(12) Contd,

4 DASH et al: PARTIAL MOLAR PROPERTIES OF DICARBOXYUC ACIDS IN AQ. ACETONE 191 Table 2- Values of ;it (mi mol-i) and SE (mi~ l mol- J l) for homologous oulic Kids in water and water + acetone (5, 10,20,30 and 40 WI k) mixture at differcotlcmperalure' - Contd. (0%,2.856) (5 4, 3.691) (10%,4.527) ;;. x 1O~ - SE X 10~ ;;. x 10= - ~ x 10= ;;.' x 10= -~x 10~ (20%,6.121 ) (30%,7.644) (40%,9.057) 20.7 (3) 1.3(6) 21.3 (4) 0.9 (5) 21.8 (7) 1.3 (5) 21.6(12) 2.3 (7) 223 (to) 2.0(7) 22.8(10) 1.9(8) 21.9(12) 2.4(10) 22.9 (11) 2.1 (9) 23.3 (10) 2.0(10) 22.7 (12) 2.3 (11) 23.6 (10) 2.1 (5) 23.9 (13) 2.6 (10) 23.3 (11) 2.2 (11) 24.3(10) 2.1 (10) 24.9(13) 2.5(11) K (0%,2.870) (5%,3.721) (10%, 4.564) 10.2(16) 2.9(4) 13.3(5) 1.2 (5) 20.6(9) 1.8 (5) 10.3(15) 2.9(7) 13.8(15) 2.8(8) 21.1 (13) 2.5 (10) 10.4 (15) 2.8 (8) 14.0(15) 2.7(9) 21.4(11) 2.0 (10) 10.6 (15,- 2.8 (8) 14.3(1-4) 3.2 (11) 21.9 (12) 2.2 (12) 10.7(15) 2.8(9) 14.1 (14) 2.7(10) 22.3(12) 2.2(12) (20%,6.161) (30%,7.705) (40%,9.144) 21.1 (3) 0.6 (5) 21.7 (8) 1.2(6) 223(9) 1.9 (8) 22.0 (12) 2.4(8) 22.7 (10) 2.2(10) 23.3(9) 1.9(10) 22.3 (11) 2.0(9) 23.3 (10) 2.1 (10) ~3.7 (10) 1.9 (10) 23.1 (12) 3.0(13) 24.1 (9) 2.8 (10) 24.4(9) 1.5 (10) 23.7(9) 3.6 (12) 24.8 (10) 1.9(11) 25A(8) 1.7 (to) K (0%,2.880) (5Wo,3.738) (10%,4.589) 10.5(15) 2.9(7) 13.4 (7) 1.2 (6) 21.0(4) 0.9(3) 10.5 (18) 3.5 (9) 13.9 (14) 2.8.{8) 21.5(13) 2.6(8) 10.6 (15) 2.8 (10) 14.2 (14) 2.8(9) 21.8 (13) 2.6(8) 10.7 (15) 2.8(10) 14.5 (14) 2.7(9) 22.3 (13) 2.6(8) 10.7 (15) 2.8 (10) 14.9(14) 2.7(9) 22.7 (12) 2.4(9) (20%,6.204) (30%, 7.774) (40%,9.239) 21.5 (5)' 0.6(3) 22.1 (7) 1.5 (7) 22.7(9) 2.0(6) 22.4(12) 2.4(9) 23.1 (11) 2.0(9) 23.7(9) 1.9 (6) 22.7 (12) 2.4(9) 23.8 (11) 2.3(11) 24.2(9) 1.8 (6) 23.6 (15) 2.4(8) 24.5 (10) 2.2(10) 24.8 (12) 2.6(8) 24.2 (12) 2.3 (7) 25.2 (10) 2.2 (10) 25.9(9) 1.8 (7) 'Values here are temperature, wt % acetone and 10 4 ao. The figures in parentheses in ;3. and SE are standard deviation with an order of 10-4

5 192 INDIAN J CHEM, SEe. A, MARCH 1996 Table3-Values of constants a and b of Eq. (10) and a', b' of Eq. (11 ) for homologous oxalic. acids in water and water + acetone (5, 10,20,30 and 40 wt %) mixture Glutaric. acid o wt % acetone a b x (3) 1.2(2) H.4(3) 1.2(2) 21.5 (3) 1.3 (2) 32.4 (2) 1.3 (2) 42.3 (3) i.3 (2) 1.4 (3) 11.0 (3) 21.8 (4) 29.8(2) 37.3 (3) 1.3 (4) 10.5 (4) 20.8 (3) 29.6 (4) 37.2(3) 1.2 (3) 10.2 (3) 19.1 (3) 28.5 (2) 33.6 (3) 0.9(3) 9.6(4) 18.6 (3) 27.4 (3) 35.4.(3) 0.6 (2) 6.8.(4) 14.5 (4) 22.8(4) 31.5 (2) 5 wt % acetone 1.1 (2) 1.1 (2) 1.1(2) 1.2 (2) 1.3 (2) 10 wt % acetone 1.0 (2) 1.0(2) 1.1 (2) J.1 (2) 1.2 (2) 20 wt % acetone 0.9 (2) 1.0 (2) i.i (2) 30 wt % acetone 0.8 (2) 0.8(2) 0.9 (2) 1.0 (2) 40 wt % acetone 0.6(3) 0.7 (2) 0.8 (2) 8.1 (7) 8.8(4) 8.9(6) 9.0(6) 9.1 (5) 8.3 (1) 8.5 (6) 8.6 (8) 8.8(6) 8.9(5) 8.4(11) 8.8 (2) 8.9(2) 9.2 (5) 9.3 (3) 8.8 (10) 9.5 (2) 9.5 (3) 9.7(3) 9.8 (2) 8.9 (I) 9.7(5) 10.1 (2) 10.4 (2) 10.6 (1) 9.0(1) 9.8 (1) 10.1 (1) 10.6 (1) 10.8 (11) b' X (3) 0.5 (2) 0.5 (2) 0.3.(3) 0.5 (3') 1.6 (2) 1.7 (2) 1.7 (2) 1.8 (3) 1.9 (3) 3.9 (5) 4.0(4) 4.1 (3) 4.1 (3) 4.2 (3) 4.0(4) 4.1 (4) 4.1 (3) 4.4(3) 4.5(3) 4.2 (3) 4.2(3) 4.3 (3) 4.5 (3) 4.6 (3) 4.3 (3) 4.4 (3) 4.4 (3) 4.5 (3) 4.7 (4) The figures in parentheses in a, b, a' and b' are the standard deviations in the order of 10-1,10-\ lo-4 and respectively. 80..~60::~~=:::==::=~(5) (4) ~540 (3) 0-,,t~~::=~~==~==::; (~ '& 20 (1) ol-~~----~~~--~~-- o % ("'/UI) Acetone Fig. 1- Plot of limiting apparent molar volume (f/j," em" mol " '] versus % (w/w) acetone at K (1) oxalic acid; (2) malonic acid; (3) succinic acid; (4) glutaric acid and (5) adipic acid The apparent molar expansibility rpe of the acids was calculated using Eq. (5) (ref. 4) rpe = aorpy + (a - ao)-- c... (5) The ~E data were fitted by a method of least squares to Eq. (6) A.=A.o+Sc 'f'e 'f'e l12 E... (6) to obtain rp~ and SE' The values of tp~and SE are presented in Table 2. In Eq. (5),. ao and a are the coefficients of thermal expansion of solvent and solution, respectively, and are given" by Eqs (7) and (8), ao = - do- 1 (bdolijt)p a= <d :' (ijdlijt)p... (7)... (8) The coefficients of thermal expansion for acid solutions in different solvents at K and 1 atm pressure are given by Eq. (9) a = ao + C c l12 + DC 312. (9) The values of ao are tabulated in Table 2. The positive and large values of S; (Table 1) for all the acids in all solvents at. the experimental temperatures indicate the presence of strong ionion interactions varying with change of temperature and acid. The ion-ion interactions are more in the mixed solvents than in water. At a particular temperature S; decreases as the hydrophobic chain length (CH 2 groups) increases, whereas, an increase in temperature increases S; slightly. The rp,o values (Table 1) are also positive and large for the studied acids in all solvents at the four temperatures indicating the presence of strong ion-solvent interactions at infinite dilution (as ion-ion interactions vanish at infinite dilution). it was found that the yo increased with increase

6 DASH et af.: PARTIAL MOLAR PROPERTIES OF DICARBOXYUC ACIDS IN AQ. ACETONE 193 Table 4-Values of :' (HOOC-COOH), t::. ~', ~ (HOOC-COOH) and t::. ~in water and water + acetone (5, 10,20,30 and 40 wt %) mixtures at different temperatures Temp. wt%," (HOOC - COOHl t::. ~'ml ((J2 f' (HOOC - COOH) Wl'l. ~ml (K) acetone (mlmol- ' ) (mol CH 2 )-1 (rnl mol "' ) (mol CH 2 )" I Intercept Exptl. Slope Exptl. Intercept Exptl Slope Exptl. ofeq.(12) Eq.(4) Eq.(12) Eq.(6) 28H (6) 36.2 (9) 11.0(l} (4) 10.1 (15) 0.1 (l) 0.1 (1) (6) 32.1 (9) IOA(2) 10.6 (9) 13.1 (8) 12.9 (5) 0.3 (6) 0.3 (5) (R) 3D.3 (9) 10.4 (4) 10.4 (12) 19.9(5) 19.R(4) OA (4) OA (4) (2) 26.3 (10) 10.5 (I) 10.4(1) 20.5(13) 20.3 (2) 0.6 (14) 0.6 (12) 30 ~2.4(5) 23.0 (II) loa (5) 10.2 (5) 21.i (9) 20.9(1 ) 0.7 (7) 0.7 (12) (2) IR.O(II) 10.5 (4) 10.2 (6) 21.6(13) 21.4 (5) 0.7 (8) 0.7 (9) 29R (3) 37.4 (9) Il.l (2) 11.0 (5) 10.2 (I) 10.2 (14) 0.1 (1) 0.7 (1) (6) 33.2 (9) m.s (3) 10.6 (9) 13.3 (7) 13.1 (5) 0.3 (7) 0.3 (6) (8) 31.4(10) ios (4) 10.5 (12) 20.3(5) 20.2(4) OA (5) OA(6) (2) 27.4 (10) 10.5 (I) loa (I) 20.9 (13) 20.7{3) 0.6(13) 0.6 (14) (3) 23.8 (11) 10.4 (I) 10.3 (3) 21.6 (12) 21.3 (4) 0:7 (ll) 0.7 (12) (2) 18.7 (11) loa (4) 10.2 (6) 22.0(18) 2l.8 (7) 0.7(9) 0.8 (7) A (2) 38.7 (9) 11.1 (I) 11.0 (3) 1O.2(5) 10.2 (16) 0.1(1) 0.1 (1) 5 ~4.R(6) 34.3 (9) 10.7 (3) 10.7 (9) 13.4(13) 13.3 (5) 0.3 (8) 0.4(12) (8) 32.4 (10) 106 (4) 10.5 (2) 20.7 (5) 20.6 (9) 0.4 (4) OA (9) (1) 28.2(10) 10.5 (I) 10.4 (2) 21.3(15) 21.1 (3) 0.6 (15) 0.6 (12) (3) 24.5 (11) loa (I) 10.3 (2) 21.9(11) 21.7 (8) 0.7 (16) 0.8 (14) (3) 19.3 (11) 10.5 (4) 10.3 (5) 22A(19) 22.3(9) 0.7 (13) 0.8 (11) (2) 39.9 (9) 11.3 (4) 11.0 (6) 10.4 (7) 10.5 (15) 0.1 (1) 0.1 (1) (6) 35.4 (9) 10.7 (3) 10.8 (9) 13.5 (8) 13A (9) 0.3 (6) OA (9) (7) 33A(IO) 10.6 (4) 10.6 ((2) 21.1 (5) 21.0 (4) OA (5) OA (9) (2} 29.1 (11) 10.5 (1) 10.5 (2) 21.6(15) 21.5 (5) 0.6(12) 0.7 (13) (2) 25.3 (11) 10.5(1) 10.4(3) 22.4(11) 22.1 (7) 0.7(9) 0.8(14) (3) 19.9 (12) 10.5 (3) to.3 (6) 22.8 (18) 22.7 (9) 0.7 (13) 0.8 (IS) T.he figures in parentheses in ~', t::. ~'are standard deviations with an order to - I and ~ and I'l. ~ are standard deviations with an order in temperature. The temperature dependence of tpvo for the acids in various solvents follows Eq. (10),... (10) over the temperature range to K where a and b are the constants and given in Table 3. Since the increase in tpvo with increase in temperature is attributed to increase in solvation, the solvation is found to be more in aqueous medium than in aqueous acetone media indicating that the. cavity occupation of crystal lattice (of the acids) by water molecules is more in pure water than in water + acetone mixtures and decreases as the water content in the mixed solvent decreases. The variation of tpvo with acetone content in the mixed solvent (i.e., with decrease in dielectric constant) is shown in Fig. 1. The results suggest that the presence of ion-solvent interaction between the molecules produces a greater structure-making effect of the acids in aqueous medium than in aqueous acetone media. As expected, the tpvo increases with increase in hydrophobic chain length. The tp~ (Table 2) increases with increase in temperature indicating the presence of caging or packing effect! in aqueous and binary aqueous solvents. As is seen, the ~ increases with increase in acetone content in the mixed solvent. The results, however, suggest that the structure making effect of the acids is favoured in aqueous medium in comparison with that in the mixed solvents. As observed, the tp2 tends to increase with increase in hydrophobic chain length indicating

7 194 INDIAN J CHEM, SEe. A, MARCH 1996 tho increasing tendency of packing effect. The temperature dependence of ~ for the acids in various solvents have been represented by Eq. (11), ~= a'+ bt... (11) Over the temperature range, to K, where a' and b' are the constants and shown in Table 3. It is of interest to examine the additive substituent effects for (p:' values of the homologous acids in water. and water + acetone mixtures. Equation (12), vo(ch 2 )x= vo(hooc-cooh)+x~ vo... (12) where x = 0, 1, 2, 3 or 4, can be used satisfactorily to express v o values of the acids in various solvents. The values of v o and ~ v o thus obtained are given in Table 4 along with those of ~ and ~ ~ obtained' by similar procedure. The ~ v o and!l. ~ values calculated from the experimental data are also shown in Table 4, and are in good agreement with the slope values. As observed, the vo(hooc-cooh) obtained from Eq. (12) closely agrees with that derived from Eq. (4) (Table 1). The!l. vovalues show an average value of 10.9 ml (mol CH 2 t I for CH 2 group increase at infinite dilution in water. This average value of 10.9 ml (mol CH 2 t I is somewhat less than the value of 12.6 ml (mol CH 2 )-1 calculated from the reported ~ ~ values of Hoiland" for homologous monocarboxylic acids in water but is in reasonably good agreement with 11.8 ml (mol CH2)-1 calculated for homologous dicarboxylic acids in water". As far as the comparison with homologous series of amines is concerned, it is observed that our value of 10.9 ml (mol CH 2 t 1 for homologous dicarboxylic acids in water at K is larger than the values of 5.4, 4.4 and 3.9 ml (mol CH 2 t I calculated for primary, secondary and' tertiary amines", respectively, in water at this temperature. Such a large difference in!l. v o values between the homologous series of amines and carboxylic acids can be attributed to the different orientation of water molecules around the charged nitrogen center (in amines) and charged carboxylate group (in acids). The opposed behaviour of expansibility and viscosity of solutions of +- salts of RNH3 and RCOO- (ref. 9) would seem to confirm this view. As observed (Table 4),!l. v o values for CHz group increase at infinite dilution in water decrease with increasing acetone content in the mixed solvent. The lowering of!l. voindicates the decreasing tendency of solute-solvent interaction and hence solvation as the acetone content in the mixed solvent increases. References 1 Dash U N & Nayak S K, Thermochim Acta, 32 (1979) 331; 34(1979) Kaulgud M V & Patil K J, J phys Chern, 80 (1976) Robinson R A & Stokes R H, Electrolyte solutions (Butter Worths Scientific Publications, London), 1955, p. JO. 4 Harned H S & Owen B B, The physical Chemistry of electrolytic solutions, 3rd Edn (Reinhold Publishing corporation, New York), 1958, p Millero F J; Structure and Transport Processes in Water and aqueous solutions, edited by R A Horne (Wiley Interscience, New York), 1971, p Hoiland H, J chem Soc Faraday Trans, 71 (1975) Hoiland H, J chem Soc Faraday Trans, 70 (1974) Cabani S, Mollica V, Lepori L & Lobo S T, J phys Chern, 81 (1977) 982, Sakurai M, Komatsu T & Nakagawa T, Bull chem Soc, Japan, 48.( 1975) 3491.